Tidal volume during pregnancy tends to do what?

• A. Increases 10 to 20%
• B. Increases 30 to 40%
• C. Decreases 10 to 20%
• D. Remains unchanged

Answer: (B)

Ventilatory adaptations in pregnancy elevate tidal volume to meet the fetus’s and mother’s increased oxygen needs and to remove CO2 more efficiently. The hormonal rise, especially progesterone, increases the respiratory center’s sensitivity to CO2, so the drive to breathe is stronger. To accommodate this without rushing breaths, tidal volume expands while the breathing rate stays about the same or may drop slightly. This combination raises overall ventilation and typically lowers arterial CO2, which is a normal finding in pregnancy. The extent of this increase is about 30% to 40% over nonpregnant values, even as the diaphragm rises and some lung volumes decrease.